Hangar bar

ABSTRACT

A hangar bar for a cathode plate and a method of producing a cathode for electrolytic recovery of metal. The hanger bar comprises a support element which is preferably stainless steel and hollow. An electrically conductive metal cladding is affixed the stainless steel bar by any appropriate mechanism, eg interference fit, welding, chemical or mechanical fastening or coextrusion or roll forming. Affixing the cladding to the stainless steel support element has significant advantages over conventional electroplating techniques including that a more precise engineering specification can be applied to the cladding thickness. This is important to maintain vertical alignment of the cathode plate in the electrolytic cell.

TECHNICAL FIELD

The present invention relates to cathodes used in electrolytic recoveryof metals. 1. Background Art

Any discussion of the prior art throughout the specification should inno way be considered as an admission that such prior art is widely knownor forms part of common general knowledge in the field.

There are various processes and apparatus for electro-refining orelectro-winning of metal. One particularly successful process forelectro-depositing of copper, for example, is the so called ISA PROCESS.In this process, stainless steel cathode mother plates are immersed inan electrolyte bath with copper anodes. The copper from the anodesdissolve into the electrolyte and are subsequently deposited in arefined form onto the blade of the mother plate. The electrolyticallydeposited copper is then stripped from the blade by first flexing thecathode plate to cause at least part of the copper deposit to separatefrom the blade, and then wedge stripping or gas blasting the remainderof the copper from the blade.

The cathode mother plate generally consists of a stainless steel blade,and a hanger bar connected to the top edge of the blade to hold andsupport the cathode in the electrolytic bath.

There are a wide variety of hanger bar constructions. Early cathodeplates used solid copper hanger bars which provided not only excellentelectrical conductivity but adequate strength to support both thecathode plate and the metal deposited thereon. It was discovered,however, that under repeated use both in the electrolytic bath and inthe stripping machinery the relatively ductile copper bar tended to bendor be damaged.

In addition, connection of the stainless steel blade to the copperhanger bar was sometimes difficult. To overcome this difficulty, complexconstruction and welding techniques were required. In one instance, asdiscussed in U.S. Pat. No. 5,492,609, additional parallel grooves weremachined in the hanger bar on either side of the central groove whichaccepts the cathode blade. The cathode blade and the hanger bar werethen welded together along this inset groove, the ridges formed betweenthe parallel grooves and the sheet then being used as welding material.This process sometimes required the copper hanger bar and steel cathodeblade to be welded in a thermally conductive liquid to maintain the barat a constant uniform temperature.

The cost, complexity and durability of the copper hanger bar led theindustry to use iron or steel hanger bars for greater structuralstrength. In most cases, while structural integrity was good, the ironor stainless steel was a poor conductor of electricity. Accordingly, inanother technique a coating of electrically conductive metal waselectrolytically deposited on the hanger bar. Such iron or steel hangerbars with electrolytically deposited conductive metal, came in variousshapes such as simple solid beams, I-beams or hollow sections.

Once again, however, it was found that these new configurations hadtheir own difficulties. Firstly, such a coating technique only permitstolerances within the technical limitation of the electroplatingprocess. The thickness and adhesion of the metal coating is additionallylimited by the electroplating process.

It is an object of the present invention to overcome or ameliorate atleast one of the disadvantages of the prior art, or to provide a usefulalternative. 2. Disclosure of the Invention

In a broad aspect, the present invention provides a hanger bar for acathode plate used in electrolytic recovery of metal comprising acorrosion resistant support element adapted for connection to a blade ofthe the cathode plate, at least a portion of said support having anelectrically conductive metal cladding affixed thereto.

The support element should be resistant to corrosion in the environmentof use, ie in the electrolytic bath. Preferably, the corrosion resistantsupport element is made from stainless steel and is preferably hollow.

The electrically conductive metal cladding may be affixed to and cover aportion or the entire exterior of the stainless steel support. This isaccomplished by any suitable technique eg an interference fit, welding,chemical or mechanical fastening, roll forming, etc.

The use of stainless steel as the support element imparts strength, longterm durability and corrosion resistance for the hanger bar. Thesefeatures are clearly important in obtaining an extended operational lifefor the hanger bar. However, as is well known in the art, stainlesssteel is a relatively poor electrical conductor. The introduction of anelectrically conductive metal cladding will permit the ready transfer ofelectrical current along the hanger bar into the blade of the cathodeplate.

However, unlike the prior art this electrical conductivity is achievedby affixing a cladding of electrically conductive material. Mechanicallyfitting the cladding permits a more precise engineering specification tobe applied to the cladding thickness and consequently aids in themaintaining vertical alignment of the cathodes in the electrolyticcells. As discussed above, tolerances now required for operation ofelectrolytic cells at high current density cannot be easily achieved byother conventional mechanisms such as electroplating of the stainlesssteel hanger bar.

In addition, the necessary strength for the hanger bar cannot beobtained from the use of copper alloy within the hanger barconstruction.

In a preferred embodiment, the electrically conductive claddingsurrounds the exposed portions of the support element, and extends partway down from the support element along the blade of the cathode. Thisembodiment reduces the electrical resistance to current passing throughthe bar onto the blade and in addition reduces the possibility ofbi-metallic corrosion of the joint between the electrically conductivemetal and the cathode blade which is normally made from stainless steel.

In addition to the aforementioned advantages arising from use of thehanger bar, the production of the hanger bar itself is much simpler thatconventional mechanisms. For instance, it is not necessary to use aportion of the hanger bar as weld material. Nor is it necessary toelectroplate the hanger bar. As will be known to persons skilled in theart, in one conventional technique, for production of the cathode plate,after the hanger bar is welded to the cathode blade, the entire assemblyis inverted and dipped into an electrolytic bath a sufficient depth toelectroplate the hanger bar with a conductive metal. The cost andhandling difficulties associated with this mechanism are clear. Affixinga cladding of electrically conductive metal to the support element ismuch simpler, more cost effective and more accurate than currenttechniques.

In a second embodiment, the present invention provides a method ofproducing a cathode plate for electrolytic recovery of metal comprisingproviding a cathode blade, connecting a corrosion resistant supportelement to the cathode blade and affixing a cladding of electricallyconductive metal to the support element.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words ‘comprise’, ‘comprising’, and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the accompanying drawings in which:

FIG. 1 is a front elevational view of a cathode plate incorporating thehanger bar of the present invention,

FIG. 2 is a sectional view through section A-A of FIG. 1 showing thehanger bar in use according to a first embodiment of the presentinvention, and

FIG. 3 is a cross sectional view showing the hanger bar and cathodeblade according to a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As shown in FIG. 1, a cathode plate 1 comprises a hanger bar 10 and acathode blade 20. Windows 15 are cut from the cathode blade 20 to assistin lifting and transportation of the cathode 1.

As mentioned above, when electro-refining copper according to the ISAPROCESS, the cathode blade 20 is a stainless steel blade. However, itwill be appreciated that the blade can be manufactured from any suitablematerial. Titanium and other metals may be used in electro-refiningoperations.

As shown more clearly in FIG. 2, the hanger bar 10 comprises a supportelement 22 with a cladding 24 of electrically conductive metal affixedthereto.

In this embodiment the support element 10 is stainless steel bar. Thestainless steel bar 22 is hollow but is preferably sealed at the ends.It is not essential that the stainless steel bar 22 be hollow.

The cladding of electrically conductive material 24, in this examplecopper, is affixed around the stainless steel bar 22. This sleeve actsto conduct electricity from the electrical connections in theelectrolytic bath through the hanger bar to the cathode blade.Typically, the cladding would be around 2 to 4 mm thick.

Welds 26 run along the terminating edge of copper cladding 24 connectingthe copper sleeve to the plate/bar assembly. The Applicant has foundthat any welding material is suitable provided it can withstand theelectrolytic environment in which the cathode plate is used. Aluminiumbronze and silicone bronze are particularly suitable weld metals.

It should be noted that the cladding may be affixed to the supportelement by a variety of techniques including interference fit, chemicalor mechanical fastening or roll forming.

As shown in FIG. 3, the sleeve may include an extension 28 onto thecathode plate 10. The intention of this extension is to reduceelectrical resistance between the hanger bar and the copper blade, andreduce bi-metallic corrosion between the hanger bar and the plate.Preferably, this extension terminates on or about the level of windows23 or 30 to 40 mm above the level of electrolyte.

The Applicants have surprisingly found that affixing the electricallyconductive metal cladding to a stainless steel support element hassignificant advantages over conventional electroplating systems.

The separate manufacture and subsequent affixing of the cladding to thesupport element provides for closer tolerances and a more preciseengineering of the cladding thickness. This is important to maintainvertical aligment of the cathode plate in the electrolytic cell whenresting on the electrical connectors either side of the electrolyticbar.

No current process allows such fine tolerances to be applied to thehanger bar construction and as far as the applicant can ascertain thisafixing of the electrically conductive sleeve over the stainless steelhanger bar has not been proposed to date.

In addition, having a stainless steel core, the bar will retain longterm mechanical strength with ease of manufacture. It will also beappreciated that this construction has advantages in terms ofmaintenance. For instance, if the sleeve/cladding of conducting materialis damaged, it is a simple matter to remove the cladding and replace.This can also be applied to current hanger bars with electrolyticcoatings of conductive material. If these coatings are damaged or it isfound that the cathode plate is not performing adequately in the celldue to poor alignment, the present invention allows precise tolerancesto be applied to the hanger bar not only to repair the hanger bar butprovide a more precise engineering of the cladding thickness and hencealignment of the cathode plate in the bar.

The hanger bar and method of production may be embodied in other formswithout departing from the spirit or scope of the present invention.

1. A cathode plate for electrolytic recovery of metal said plateincluding a cathode plate and a hanger bar, said hanger bar comprises acorrosion resistant support element connected to the blade at thecathode plate and an electrically conductive metal cladding affixedthereto, the electrically conductive metal cladding extending over atleast a portion of the support element to the cathode blade and part waydown the cathode blade.
 2. A cathode plate as claimed in claim 1,wherein the support element is constructed from stainless steel.
 3. Acathode plate as claimed in claim 1, wherein said support element ishollow.
 4. A cathode plate as claimed in claim 1, wherein theelectrically conductive metal cladding is affixed such that it coversthe entire exterior of the support element.
 5. A cathode plate asclaimed in claim 1, wherein the electrically conductive metal claddingis affixed such that it covers a portion of the support element.
 6. Acathode plate as claimed in claim 1, wherein the electrically conductivemetal cladding is affixed by an interference fit.
 7. A cathode plate asclaimed in claim 1, wherein the electrically conductive metal claddingis affixed by welding.
 8. A cathode plate as claimed in claim 7, whereinthe electrically conductive metal cladding is welded to the supportelement and/or cathode blade by aluminium bronze weld.
 9. A cathodeplate as claimed in claim 7, wherein the electrically conductive metalcladding is welded to the support element and/or cathode blade bysilicone bronze weld.
 10. A hanger bar claimed in claim 1, wherein theelectrically conductive metal cladding is affixed to the support elementby mechanical and/or chemical fastening.
 11. A cathode plate as claimedin claim 1, wherein the support element and electrically conductivemetal cladding are affixed by coextrusion.
 12. A cathode plate asclaimed in claim 1, wherein the electrically conductive metal claddingis affixed to the support element by roll forming.
 13. A cathode plateas claimed in claim 12, wherein the cladding extends from the supportelement to a position 30 to 40 mm above the metal deposition area on thecathode blade.
 14. A hanger bar as claimed in claim 1, wherein the bladeis stainless steel.
 15. A hanger bar as claimed in claim 1, wherein theelectrically conductive metal is copper.
 16. A method of producing acathode plate for electrolytic recovery of metal comprising a cathodeblade, connecting a corrosion resistant support element to the cathodeblade, said element being adapted to support the cathode plate in anelectrolytic bath, and affixing a cladding of electrically conductivemetal to the support wherein the electrically conductive metal claddingextends over at least a portion of the support element to the cathodeblade and part way down the cathode blade.
 17. A method as claimed inclaim 16, wherein the cladding is affixed to the support element afterconnection of the support element and cathode blade.
 18. A method asclaimed in claim 16, wherein the cladding is affixed to the supportelement before connection of the support element to the cathode blade.19. A method as claimed in claim 16, wherein the electrically conductivemetal cladding is affixed by an interference fit.
 20. A method asclaimed in claim 16, wherein the electrically conductive metal claddingis affixed by welding.
 21. A method as claimed in claim 20, wherein theelectrically conductive metal cladding is welded to the support elementand/or cathode blade by aluminium bronze weld.
 22. A method as claimedin claim 20, wherein the electrically conductive metal cladding iswelded to he support element and/or cathode plate by silicone bronzeweld.
 23. A method as claimed in claim 16, wherein the electricallyconductive metal cladding is affixed by chemical or mechanicalfastening.
 24. A method as claimed in claim 16, wherein the support andelectrically conductive metal cladding are affixed by roll forming. 25.A method as claimed in claim 16, wherein the cathode blade and/orsupport element are constructed from stainless steel.
 26. A method asclaimed in claim 16, wherein the electrically conductive metal iscopper.